In a Long Term Evolution (Long Term Evolution, LTE for short) system, a terminal device performs radio resource management (Radio Resource Management, RRM for short) measurement based on a reference signal (Reference Signal, RS for short). If quality of a serving cell of the terminal device reaches a threshold, the terminal device stops measuring an intra-frequency neighboring cell to save power. If quality of a serving cell is lower than a threshold, the terminal device starts measuring an intra-frequency neighboring cell, to find a better intra-frequency neighboring cell. However, in the prior art, when calculating cell quality, a terminal device detects beams of a cell based on a quantity N of beams that need to be measured and that are specified by a network side, and detects a quantity M of beams whose signal quality exceeds a threshold. If M is greater than N, quality of N beams with best quality is averaged to obtain the cell quality. If M is less than N, quality of the M beams is averaged to obtain the cell quality. Cell quality obtained by averaging beam quality is inaccurate.
In a 5th generation mobile communications (5th-Generation, 5G for short) system, a terminal device does not perform RRM measurement based on an RS any more, but performs RRM measurement based on a synchronization signal (Synchronization Signal, SS for short). However, in the prior art, there is no specific implementation of measurement based on a synchronization signal.